A typical conventional light-emitting apparatus turns on an LED as in the following manners. A resistor and an LED are connected in series to a constant-voltage power supply so that the resistor can adjust the current passing through the LED. Alternatively, as illustrated in FIG. 12(A), a current limiter circuit is connected between a constant-voltage power supply 1 and an LED 2 in series so that the current limiter circuit can adjust the current passing through the LED. However, when a resistor or a current limiter circuit is connected in series, the inserted resistor or current limiter circuit serves as a load during normal operation of the LED, causing energy loss.
In recent years, LEDs have had increasingly high brightness, and unlike conventional LEDs for indication purposes, it has been necessary to operate the LEDs at high current. In the case where the LEDs are driven at high current, energy loss resulting from the load because of the inserted resistor or the inserted current limiter circuit will increases if the apparatus has the same configuration as the typical conventional light-emitting apparatus. In order to reduce such energy loss and also to accelerate device size reduction, it has become more common to use a constant-current power supply in place of a constant-voltage power supply.
Conventional common power supplies have a capacitor between the reference potential terminal and the output terminal in order to supply stable voltage and current and to reduce fluctuation due to noise or the like (see, for example, Patent Document 1). In this capacitor, electric charge according to the capacity of the capacitor and the output voltage of the constant-current power supply is stored during the operation of the constant-current power supply. Even after the operation is stopped, electric charge is kept stored until electric charge is completely released by self-discharge.
In a typical conventional light-emitting apparatus that lights an LED 2 by electric power from a common constant-current power supply 1, the constant-current power supply 1 and the LED 2 are connected to each other by wiring, as illustrated in FIG. 12(B). In such a case, when the LED 2 is mounted while electric charge is being stored in a capacitor C1, the LED 2 may break or deteriorate. The reason is that, although only a current with a predetermined current value is supplied from the current limiter circuit, electric charge stored in the capacitor C1 is discharged instantly when the LED 2 is mounted, and therefore a very high current (instantaneous current) passes therethrough instantaneously.    [Patent Document 1] JP 2004-119078 A